metformin

ROUTE	ONSET	PEAK	DURATION
PO-IR	unknown	unknown	12 hr
PO-ER	unknown	4–8 hr	24 hr

Contraindicated in:

Hypersensitivity;
Metabolic acidosis (including diabetic ketoacidosis);
Severe renal impairment (CCr <30 mL/min);
Iodinated contrast imaging procedure in patients with CCr 30–60 mL/min; a history of liver disease, alcoholism, or heart failure; or those who will be administered intra-arterial iodinated contrast (discontinue metformin and reevaluate renal function 48 hr after imaging procedure; may restart therapy if renal function stable);
Hepatic impairment;
Lactation: Lactation.

Use Cautiously in:

Mild to moderate renal impairment (initiation of therapy not recommended if CCr 30–45 mL/min; if CCr becomes <45 mL/min during therapy, assess risk-to-benefit of continuing therapy);
Chronic alcohol use/abuse;
Hypoxic states (acute HF, shock, MI, sepsis; discontinue metformin);
Surgery (temporarily discontinue metformin when food and/or fluid intake is restricted);
Pituitary deficiency or hyperthyroidism;
OB: Insulin recommended during pregnancy;
Pedi: Safety and effectiveness not established in children 18 yr (extended release) or 10 yr (immediate release);
Geri: Older adults may be at risk of lactic acidosis.

Adv. Reactions/Side Effects ⬆ ⬇

F and E: LACTIC ACIDOSIS

GI: abdominal bloating, diarrhea, nausea, vomiting, unpleasant metallic taste

Hemat: ↓vitamin B₁₂ levels

Interactions ⬆ ⬇

Drug-drug:

Acute or chronic alcohol ingestion or iodinated contrast media↑ risk of lactic acidosis.
Amiloride, digoxin, morphine, procainamide, quinidine, triamterene, trimethoprim, calcium channel blockers, and vancomycin may compete for elimination pathways with metformin. Altered responses may occur.
Cimetidine and furosemide may ↑ effects of metformin.
Nifedipine↑ absorption and effects.

Drug-Natural Products:

Glucosamine may worsen blood glucose control.
Chromium and coenzyme Q-10 may produce ↑ hypoglycemic effects.

Route/Dosage ⬆ ⬇

PO (Adults ): Immediate-release tablets: 500 mg twice daily; may ↑ by 500 mg at weekly intervals up to 2000 mg/day. If doses >2000 mg/day are required, give in 3 divided doses (not to exceed 2500 mg/day) or 850 mg once daily; may ↑ by 850 mg at 2-wk intervals (in divided doses) up to 2550 mg/day in divided doses (up to 850 mg 3 times daily); Extended-release tablets: 500 mg once daily with evening meal; may ↑ by 500 mg at weekly intervals up to 2000 mg once daily.
PO (Children 10–17 yr): Immediate-release tablets: 500 mg twice daily; may be ↑ by 500 mg/day at 1-wk intervals, up to 2000 mg/day in 2 divided doses.

Availability ⬆ ⬇

(Generic available)

Immediate-release tablets: 500 mg; 625 mg; 850 mg; 1000 mg
Extended-release tablets (Glumetza): 500 mg; 750 mg; 1000 mg
Oral solution (Riomet)cherry flavor: 500 mg/5 mL
In combination with: alogliptin (Kazano); canagliflozin (Invokamet, Invokamet XR); dapagliflozin (Xigduo XR); empagliflozin (Synjardy, Synjardy XR); empagliflozin and linagliptin (Trijardy XR); ertugliflozin (Segluromet); glipizide (generic only); glyburide (generic only); linagliptin (Jentadueto, Jentadueto XR); pioglitazone (Actoplus Met); saxagliptin (generic only); and sitagliptin (Janumet, Janumet XR, Zituvimet, Zituvimet XR). See Appendix [not included in this PDA edition].

Assessment ⬆ ⬇

When combined with oral sulfonylureas, observe for signs and symptoms of hypoglycemia (abdominal pain, sweating, hunger, weakness, dizziness, headache, tremor, tachycardia, anxiety).
Patients whose blood sugar has been well controlled on metformin who develop illness or laboratory abnormalities should be assessed for ketoacidosis or lactic acidosis. Assess serum electrolytes, ketones, glucose, and, if indicated, blood pH, lactate, and pyruvate levels.If acidosis occurs, discontinue metformin immediately and provide appropriate medical treatment. Patients with severe renal impairment are at greatest risk for lactic acidosis.

Lab Test Considerations:

Monitor serum glucose and A1c periodically during therapy to evaluate effectiveness of therapy. May cause false-positive results for urine ketones.
- Assess renal function before starting and at least annually during therapy. Monitor patients at risk for renal impairment more frequently. Discontinue metformin if renal impairment occurs.
- Monitor serum folic acid and vitamin B₁₂ levels every 1–2 yr in long-term therapy. Metformin may interfere with their absorption.

Implementation ⬆ ⬇

Do not confuse metformin with metronidazole.
Patients stabilized on a regimen for diabetes who are exposed to stress, fever, trauma, infection, or surgery may require administration of insulin. Withhold metformin and reinstitute after resolution of acute episode.
- Temporarily discontinue metformin in patients requiring surgery involving restricted intake of food and fluids. Resume metformin when oral intake has resumed and renal function is normal.
- Hold metformin before or at the time of studies requiring IV administration of iodinated contrast media and for 48 hr after study.
PO: Administer metformin with meals to minimize GI effects.
- DNC: Extended-release tablets must be swallowed whole; do not crush, dissolve, or chew. Administer Glumetza with the evening meal.

Patient/Family Teaching ⬆ ⬇

Instruct patient to take metformin at the same time each day, as directed. Take missed doses as soon as possible unless almost time for next dose. Do not double doses. Instruct parent/caregiver to read the Medication Guide prior to use and with each Rx refill as changes may occur.
Explain to patient that metformin helps control hyperglycemia but does not cure diabetes. Therapy is usually long term.
Encourage patient to follow prescribed diet, medication, and exercise regimen to prevent hyperglycemic or hypoglycemic episodes.
Review signs of hypoglycemia and hyperglycemia with patient. If hypoglycemia occurs, advise patient to take a glass of orange juice or 2–3 tsp of sugar, honey, or corn syrup dissolved in water, and notify health care professional.
Instruct patient in proper testing of blood glucose and urine ketones. These tests should be monitored closely during periods of stress or illness and health care professional notified if significant changes occur.
Explain to patient the risk of lactic acidosis and the potential need for discontinuation of metformin therapy if a severe infection, dehydration, or severe or continuing diarrhea occurs or if medical tests or surgery is required. Symptoms of lactic acidosis (chills, diarrhea, dizziness, low BP, muscle pain, abdominal pain, sleepiness, slow heartbeat or pulse, dyspnea, or weakness) should be reported to health care professional immediately.
Advise patient to notify health care professional of all Rx or OTC medications, vitamins, or herbal products being taken and to consult with health care professional before taking other medications or alcohol.
Inform patient that metformin may cause an unpleasant or metallic taste that usually resolves spontaneously.
Inform patients taking extended-release tablets that inactive ingredients resembling the tablet may appear in stools.
Advise patient to inform health care professional of medication regimen before treatment or surgery.
Advise patient to report the occurrence of diarrhea, nausea, vomiting, and stomach pain or fullness to health care professional.
Advise patient to carry a form of sugar (sugar packets, candy) and identification describing disease process and medication regimen at all times.
Rep: Insulin is the recommended method of controlling blood glucose during pregnancy. Advise females of reproductive potential to notify health care professional promptly if pregnancy is planned or suspected or if breastfeeding. Caution patient that metformin may result in ovulation in some anovulatory women, leading to unintended pregnancy.
Emphasize the importance of routine follow-up exams and regular testing of blood glucose, A1c, renal function, and hematologic parameters.

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Pronunciation ⬇

Classifications ⬆ ⬇

Indications ⬆ ⬇

Action ⬆ ⬇

Pharmacokinetics ⬆ ⬇

Time/Action Profile ⬆ ⬇

Contraind./Precautions ⬆ ⬇

Adv. Reactions/Side Effects ⬆ ⬇

Interactions ⬆ ⬇

Route/Dosage ⬆ ⬇

Availability ⬆ ⬇

Assessment ⬆ ⬇

Implementation ⬆ ⬇

Patient/Family Teaching ⬆ ⬇

Evaluation/Desired Outcomes ⬆ ⬇

US Brand Names ⬆ ⬇

Canadian Brand Names ⬆ ⬇

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